The present invention relates to a non-destructive inspection apparatus for heat-transfer tubes in boilers.
Heat-transfer tubes in boilers, which become thinner in thickness due to wear, corrosion and the like, are periodically inspected so as to measure the thickness of each heat-transfer tube.
To this end, conventionally a temporary scaffold is assembled in the boiler furnace upon inspection and an inspector stands on the scaffold to measure the thickness of each heat-transfer tube from exterior thereof.
The inspection system of this type has been proved to have the following problems:
(i) Since assembling a temporary scaffold is involved, inspection time becomes longer and inspection cost becomes expensive due to extra materials and labor required. PA0 (ii) Inspection work is dangerous since an inspector must accomplish the inspection while standing on a temporary scaffold which is unstable. PA0 (iii) Because of inspection in burnt-gas passages, inspection environment and efficiency are adversely affected by dust and the like accumulated.
To overcome these problems, there has been proposed a system in which, as shown in FIG. 1, an inspection hole 3 is formed through a side face of a header 2 for boiler heat-transfer tubes 1. Inserted through the hole 3 is a guide 4 through which in turn a wall-thickness measuring instrument 5 is inserted into the heat-transfer tube 1, thereby measuring the wall thickness of each heat-transfer tube 1 from interior thereof.
The measuring instrument 5 comprises a sensor 6 and a cable 8 having a plurality of spaced floats 7 and connected to the sensor 6. The measuring instrument 5 is introduced together with compressed fluid into the guide 4 so that the floats 7 behave like pistons, whereby the measuring instrument 5 is displaced.
Referring next to FIGS. 2-5, a leading portion of the guide 4 will be described. An outer guide pipe 10 having a two-piece type leading portion receives a slide frame 11 which has a two-piece type leading portion and which in turn receives in their leading portions a head 13 through a pin 14; the head 13 is provided for insertion of the measuring instrument 5 into the heat-transfer tube 1 as will be described hereinafter. The head 13 has an upper portion integrally formed with a lever 15 to which one end of a link 16 is pivotably connected with a pin. The other end of the link 16 is pivotably connected with a pin to a slide bar 17 which is slidably disposed along the slide frame 11 within the outer guide pipe 10 so that push or pull of the slide bar 17 causes the head 13 to rotate.
Furthermore, four supporting legs 19 each having a rotatable and swingable roller 18 at its leading end are pivoted in the form of a cross to a supporting-leg head 22 and are normally retained open or divergent by means of a cylindrical member 21 which is loaded with a spring 20 (see FIG. 2). Slide beams 23 are securely attached to the head 22 through bolting or the like to sandwich the same and are slidably inserted between the outer guide pipe 10 and the slide frame 11 so that the head 13 is adapted to be received between the slide beams 23 when the supporting-leg head 22 is displaced away from the head 13.
As best shown in FIG. 5, a movable head 25 is slidably fitted into a space 24 defined within the head 13. A flexible tube (vinyl tube) 26 extends through the outer guide pipe 10 and is connected to the head 13 such that one end of the tube 26 is opened at the space 24. A tension spring 27 is loaded in the head 13 to pull the movable head 25 in the direction away from the inner surface of the header 2. An annular spacer 28 is securely interposed between the end of the flexible tube 26 and the movable head 25 in the space 24. Stoppers (not shown) are disposed such that a pressure-receiving surface of the movable head 25 and the spacer 28 are not made in contact with each other and therefore a minimum space or gap 29 is maintained between them.
An end of the guide 4 away from the head 13 has bolt holes 30 each for locking of the corresponding slide frame 11 and slide beam 23 together.
Upon measurement of the wall thickness, first the guide 4 is inserted through the inspection hole 3 at one end face of the header 2. More particularly, an inspector inserts the leading end of the guide 4 into the header 2 through the inspection hole 3 with the supporting legs 19 being manually closed or converged. Then, the inspector manually releases the supporting legs 19 to open, whereby the latter are pushed by the cylindrical member 21 under the force of the spring 20 so that a rotating surface of each roller 18 is pressed against the inner surface of the header 2 to support the guide 4. In this case, the supporting-leg head 22 is away from the head 13 so that the head 13 is being received between the slide beams 23 to be aligned with the outer guide pipe 10. Then, pushing the slide bar 17 toward the head 13 forces the lever 15 to move to an upright position through the link 16; that is, the head 13 is rotated about the pin 14 through a right angle. In this rotation, a leading portion of the flexible tube 26 which has been straight is easily bent. Thereafter, the slide beam 23 is pulled to the right in FIG. 2 so that the supporting-leg head 22 is retracted and abuts on the head 13. Bolts are screwed into the bolt holes 30 to lock the slide frame 11 with the slide beams to thereby securely hold the head 13.
After the head 13 is securely held in this manner, the position of the guide 4 is so adjusted that the movable head 25 in the head 13 is aligned with a heat-transfer-tube hole 12 of the header 2. Then, the sensor 6 and the cable 8 with the floats 7 are inserted into the flexible tube 26, utilizing the pressure of water. Therefore, as described previously, the floats 7 behave like pistons so that the measuring instrument 5 passes through the tube 26 and reaches the head 13.
When the sensor 6 and the float 7 at the leading end reach the head 13 and then pass into the movable head 25, the water pressure acts on the flanged pressure-receiving surface of the movable head 25 through the minimum space or gap 29. As a result, the movable head 25 is forced to move toward the hole 12 against the force of the tension spring 27 so that the movable head 25 is urged to contact the inner wall surface of the heat-transfer tube 1. Thus, the measuring instrument 5 is inserted into the heat-transfer tube 1 to measure the wall thickness thereof.
With the system of the type described just above, the movable head 25 is activated by water pressure so that there arises a problem that water may leak from the head 13 into the header 2.
In order to overcome this problem, there has been proposed a system for positively pressing a pressure head formed integral with the flexible tube against the inner surface of the header, thereby maintaining sealability.
In either of the above-mentioned systems, accurate alignment of the leading end of the head 13 with the heat-transfer tube 1 in the header 2 is difficult to carry out. When the leading end of the head 13 is not correctly aligned with the hole 12, leakage of the compressed fluid and/or damage of the galled parts will result. In order to overcome this problem, there has been further proposed a system in which an optical fiber or the like is inserted into the flexible tube 26 so that an inspector can accomplish the alignment of the leading end of the head 13 with the heat-transfer-tube hole 12 while watching the latter.
Even in the last-mentioned system, it is difficult to confirm correct alignment of the leading end of the head with the hole 12 of the header 2.
In view of the above, a primary object of the present invention is to easily and positively confirm alignment of the leading end of the head with the heat-transfer tube, thereby improving inspection efficiency and preventing the above and other problems such as leakage of compressed fluid.
The present invention will become more apparent from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.